Completely n00b question

[Pryda]

I think there has been a misunderstanding. I don't know what to enter on Fuelly or I must be doing it wrong. My motorcycle has a pretty good MPG but this site only says it gets 3x MPG which is completely wrong..which makes me think I'm entering my data incorrectly.

I'm not completely sure, can someone clear this up for me so I can stop wrecking my brain? I use a trip odemeter so I know how many miles my last fuelup has gotten me.

Last week I put 9.6l (£10) in and got 80miles. A few days ago I put 13.5l (£14) in and got 122 miles from it.

I don't know if you act like "well I got 80 miles last time, but now I'm putting in 13.5l for £/L" or if I enter it as "from that fuel up i got 80 miles which was from 9.6l for £/L"

You dig? This sounds so stupid but something is wrong..I definitely get more than 3x UK MPG!

[pb]

First, make sure you click the "UK" link the upper left corner of the page. That will make sure you'll looking at UK units.

So far, you've told Fuelly that you've gone about 292 miles and put in about 8.5 gallons of gas. (Sorry, US units, I know.) If you divide 292 by 8.5 you get 34.4--that's your average fuel economy in US unites. It's 40.7 UK MPG.

When you fuel up, just put in the miles on your tripometer and the amount of gas you just put in. That method works for figuring out your average fuel economy.

[Nat]

Make sure you brim your tank every time (or fill to the same point) and reset your trip - you fill up, reset your trip, then next time you fill up you can note down the miles you got on the last lot of petrol, and assuming you're brimming your tank again you will know the exact amount of petrol you used to do that mileage.

Apart from that, as pb says, make sure you're using UK mode. I thought this site was doing its calculations wrong before I noticed the US/UK modes. Turns out not everything is bigger in the US, gallons certainly aren't!

[Nat]

Looking at your bike's page you got about 57 mpg off your most recent fillup. Looking at your earlier fill-ups, and the fact you put in 13litres on an 80 mile tank, the fill-up before that can't have been a full tank.

For this site to work properly you really need to brim it every time. Try editing your earlier fill-ups to partial ones, I think that should exclude them from your average MPG number.

[Pryda]

"When you fuel up, just put in the miles on your tripometer and the amount of gas you just put in." I suppose that was too straightforward to put in the FAQ Glad that got cleared up.

I see, I don't brim it every time..will from now on. Thanks guys, very helpful.

[pb]

Thanks Nat, yeah, complete fills are an important part of how the site works. Here's more info: Why do I need to fill the tank?

[Pryda]

Wait, wait, wait. This thing couldn't be working right. If I fill in how many miles I got since last fuel up, how many litres I just put in and how much it just cost me per litre, it all seems fine. It gives me a MPG, and there we go. Only, the MPG calculated (for some reason?!) seems to take into account the number of litres *I just put in* -- why would it do that?!

[pb]

yeah, Pryda, that's how it works. If you make that calculation every time you fill your tank you get a good sense of your average mileage. It's not an exact science.

There are probably other ways to calculate your fuel economy, but this is the way we set things up for Fuelly.

[Pryda]

Hrm. I knew something was messing with my results but it took a while to put my finger on it. I don't see why the amount of fuel I put in right now affects the performance of my motorcycle in the past. It's illogical, right?

[mathowie]

We measure by difference, assuming you fill up the tank to the brim every time. If you imagine that is a maximum number, 100% (units don't matter in this example) we could every fill up for how many units you used up since it was last at 100%, and figure out how far you went to calculate your fuel economy. It's pretty simple.

If you aren't filling up the tank to full, you should check off the "partial fuel up" option and we won't calculate fuel economy for that specific fuel up, but we will for your cumulative fuel economy (which takes all your distance traveled and all fuel ever burned to calculate a total).